Re: [Xen-devel] [PATCH RFC v2 1/4] x86/mm: Shadow and p2m changes for PV mem_access

[Gianluca Guida <glguida@xxxxxxxxx>]

On Fri, Aug 22, 2014 at 10:34 AM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

I am concerned with the addition of a the vcpu specifics to
shadow_write_entries(). Most of the shadow code is already vcpu centric
where it should be domain centric, and steps are being made to alleviate
these problems.

The historical reason the code is set up this way, if you are referring to the fact that every shadow operation is vcpu-specific while the interface to it is domain specific, is due to the design choice of leaving the door open to experiment with per-vcpu shadows.

That always looked like a nice feature, I am not sure anybody ever implemented it. I would advocate -- for the sake of code consistency -- to keep the current shadow internal interfaces per-vcpu in upcoming patches, and change it when you propose your domain-centric patch, effectively killing this probably never-exploited opportunity.

Honestly, haven't been following shadow code in a while, so probably consistency has already been lost, in which case you should feel free to ignore this comment.

Gianluca

Â

 Any access in from a toolstack/device model hypercall
will probably be using vcpu[0], which will cause this logic to be
applied in an erroneous context.

~Andrew

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